Grid Tie Inverters - What's the difference? Topic is solved

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Grid Tie Inverters - What's the difference?

Post by Gregski »

please forgive me for a non EV related inquiry, but I know smarts lives here so I'm sure you can explain it to me

not sure if you heard of these solar panel grid tie inverters but they are very simple to install, you just connect some solar panels to this box and then plug the box into the wall outlet, and no batteries needed

my question is, what's the difference between the one that is 12 volts vs the one that is 24 volts, I mean if I was to tear them open what electronic component would be different

please talk to me like I'm 8 years old (I mean it)

Y&H 1000W Grid Tie Inverter Stackable MPPT Pure Sine Wave DC15-28V Solar Input AC90-140V Output for 12V Solar Panel
12v.png

Y&H 1000W Grid Tie Inverter Stackable MPPT Pure Sine Wave DC30-45V Solar Input AC90-140V Output for 24V 30V 36V PV Panel
24v.jpg
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Re: Grid Tie Inverters - What's the difference?

Post by johu »

Inside it you will find an isolated DC-DC converter and the actual sine wave inverter. DC-DC converter works much like your laptop power supply only that it turns 12V into 250V or thereabouts. It has input capacitors which might be rated different (more capacity, less voltage for the 12V model), transistors may even be the same but they do need to switch twice the current at 12V, so may be stronger or more. And finally the transformer winding ratio will be like 1:20 for the 12V model and 1:10 for the 30V model.
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

johu wrote: Fri Jul 22, 2022 3:30 pmInside it you will find an isolated DC-DC converter and the actual sine wave inverter. DC-DC converter works much like your laptop power supply only that it turns 12V into 250V or thereabouts. It has input capacitors which might be rated different (more capacity, less voltage for the 12V model), transistors may even be the same but they do need to switch twice the current at 12V, so may be stronger or more. And finally the transformer winding ratio will be like 1:20 for the 12V model and 1:10 for the 30V model.
wow you sure seem to know a lot about Inverters, ever thought about applying all you know to EVing?
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Re: Grid Tie Inverters - What's the difference?

Post by arber333 »

Gregski wrote: Fri Jul 22, 2022 3:52 pm
johu wrote: Fri Jul 22, 2022 3:30 pmInside it you will find an isolated DC-DC converter and the actual sine wave inverter. DC-DC converter works much like your laptop power supply only that it turns 12V into 250V or thereabouts. It has input capacitors which might be rated different (more capacity, less voltage for the 12V model), transistors may even be the same but they do need to switch twice the current at 12V, so may be stronger or more. And finally the transformer winding ratio will be like 1:20 for the 12V model and 1:10 for the 30V model.
wow you sure seem to know a lot about Inverters, ever thought about applying all you know to EVing?
Well i can just comment that i dont know where would openinverter be without him ;).
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Re: Grid Tie Inverters - What's the difference?

Post by johu »

Gregski wrote: Fri Jul 22, 2022 3:52 pm wow you sure seem to know a lot about Inverters, ever thought about applying all you know to EVing?
EVs will never catch on, I heard
arber333 wrote: Fri Jul 22, 2022 4:22 pm Well i can just comment that i dont know where would openinverter be without him ;).
And what would the world be without openinverter? A safer place, some say :P
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

just came across this video of a 1000 watt comparison to a 1300 watt inverter of the same brand, not exactly what I was trying to compare 12 volt vs 24 volt but the findings were surprising none the less


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Re: Grid Tie Inverters - What's the difference?

Post by evMacGyver »

Are these Chinese "grid tied" solar inverters legal anywhere?

In Finland grid tie inverter requires VDE-AR-N-4105:2018, which is newest standard. Older VDE-AR-N-4105 2011-08 inverters are not allowed anymore for new installations. And VDE0126-1-1 has never been legal.

I would not install grid tied inverter without proofed islanding protection. Which means in case of grid fails or power cut on service etc, inverter needs to stop supplying the grid. Fail to do so might even kill electrician.

If someone knows if there is external certified islanding protection modules, I would be happy to hear!
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Re: Grid Tie Inverters - What's the difference?

Post by arber333 »

This is the reason i am separating my 5kW battery solar inverter from grid tied system. Former is supplying the house after the junction with the latter.
It means i had to remodel house fuses to single phase with corresponding GFI. I only left 3phase loads such as heat pump and evse connected in the usual way.

That way if grid drops the ball battery inverter will supply the house still no danger to electicians working on the grid.
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Re: Grid Tie Inverters - What's the difference?

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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

here we go again for [ahem] SCIENCE, The Greg went out and bought a cheap AMAZON 24 volt inverter so that he can have you guys hand hold him as he performs a stare-and-compare-ectomy of the two models

IMG_5902.JPG
IMG_5904.JPG
IMG_5906.JPG

I love how you can look at one AMAZON cheap inverter description and see 3 different sets of completely different arbitrary specs
IMG_5908.JPG
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

I wanted to do this on my Hübner Junior Electronic Workbench in the privacy of my own home office, but the wife insisted I work on them on our formal dining table

IMG_5911.JPG
IMG_5912 L.jpg
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

so let's start with the DC input side and them external (pronounced: "we did a crappy job of designing this thing and now you get to replace the fuses") fuses

both units appear to be equipped with three 30 amp fuses in parallel if I understand the DC wiring correctly on the DC input side


12 volt model 24/36 volt model
IMG_5973.JPG
IMG_5937.JPG
IMG_5924.JPG
IMG_5939.JPG
IMG_5922.JPG
no pic cause it looked the same
IMG_5926.JPG
no pic cause it looked the same
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

so in order to slide the steel or pot metal bottom cover off, I stripped I mean undid four screws on each end

IMG_5914.JPG
IMG_5916.JPG
IMG_5920.JPG

I believe this is the AC output side, and I gotta tell you those three, red, white, and black wires are soooo skinny the pic doesn't do them injustice
IMG_5918.JPG

input fan sucks the air in on the AC side
IMG_5928.JPG

that's cute
IMG_5941.JPG
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

and here are the circus boards, they are the exact same MODEL: G1I-1400W number and even have the same INPUT: 11-55 VDC rating, just have a different born on date

12 volt model 24/36 volt model
IMG_5934.JPG
IMG_5968.JPG
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

here's the 24/36 volt model coming apart

IMG_5945.JPG
IMG_5943.JPG
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

mandatory stare and compare
IMG_5949.JPG
IMG_5951.JPG
IMG_5953.JPG
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

the caps appear to be the same 50v 2200uF


12 volt model 24/36 volt model
IMG_5961.JPG
IMG_5963.JPG
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

these small and large transistors appear to be the same as well, hard to see the part numbers, here's what I think they are

Small Guys
CQ1408 U2080G - 20.0 Ampere Heatsink Common Cathode Ultra Fast Recovery Rectifiers

Bigger Ones
1XFH44N50P S11855
PolarTM HiperFETTM
Power MOSFET


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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

so this leads us to the yellow brick road(s) which have different part numbers it would be great if someone could explain what their roles are, I'm thinking filters of sorts?

12 volt model 24/36 volt model
XJ1400W-PQ1028 XJ1400W-PQ2250
IMG_5930.JPG
IMG_5957.JPG
IMG_5932.JPG
IMG_5959.JPG
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Re: Grid Tie Inverters - What's the difference?

Post by lompilomp »

Those are the high frequency transformers, most high frequency inverters like this work this way:

1. low voltage dc is pulsed into these transformers at very high frequency with a bunch of low-ish voltage MOSFETS. This allows a lot of power to be put through the transformers without requiring a huge iron core. For comparison imagine the size and weight of the transformer you'd need to push 1000w continuously. Probably the size of the entire inverter.

2. The output of the transformers is rectified, possibly by discrete diodes that look like MOSFETS, or in lower power applications could be normal diodes. The thing is at this point, the voltage is around ~170vdc (for 110v inverters) and around ~340vdc for 220v inverters. Note that the dc voltage is higher than the AC voltage because AC voltage is rms, which is a sort of average, but the peak voltage of the sine wave is the DC voltage you're seeing here.

Now the good thing about these high voltages is that to get the 1000w rating, at 120v its only 8-9a going through here, so not as beefy components required in the HV section.
3. In an off-grid inverter you'd have a large-ish capacitor bank to hold the HV and stabilize it, but in a grid tie inverter its not as neccessary because there's no surges and most noise will be supressed later in the circuit.

4. Once you have your HVDC, it goes into an H-bridge, which is always in sets of 4. This is a similar concept to reversing relays, basically they are used to switch the high voltage in a certain way that they can reverse it, so you can get AC from it. Those are the IXFH44N50P transistors you see. They are 500v rated.

5. An SPWM signal is fed into the transistors, to make the output as close to a sine wave as possible. Though it needs a lot of filtering to get rid of all the switching noise.

6. Output of the transistors goes into an LC filter, which is an inductor in series with the output, and a (low capacity) capacitor after the inductor to neutral. This turns the rather noisy sine wave into a basically perfect sine wave (depending on how good the filtering is). Then it just goes out into the utility, and of course there's a lot of microcontrollers in the way, making sure it isn't overheating, outputting when theres no grid, overpowered, or the grid voltage is too high. For example, if the grid voltage is 110v, the inverter will push power in, so it might go up to 110.1v or w/e. If your grid is too weak and your grid-tie inverter is too powerful, it may raise the voltage above acceptable range and a PROPER inverter would realize and either shut down or reduce output. Now with a 1000w inverter I doubt this scenario would happen, although its entirely doable.



But yeah most likely the only difference between the two is the windings of the LV-HV transformers, I'd assume that the higher voltage one has 2x the turns but with thinner wire on the primary side. Secondary is probably the same.

Thats basically the issue with inverters, there's no one-size-fits-all when it comes to voltage ranges. IMO, the higher the voltage the better, because there's less losses the higher you go. That's why you have these solar gridtie inverters that can do 70kw that are smaller lighter and cheaper than 12kw low voltage inverters. But of course thats a different topic b/c going off-grid with high voltage is rather complicated due to having so many batteries in series, and of course the entry cost because you need a large number of solar panels in series to even get started.
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Re: Grid Tie Inverters - What's the difference?

Post by Gregski »

lompilomp wrote: Sat Aug 27, 2022 9:09 pm Those are the high frequency transformers, most high frequency inverters like this work this way:

1. low voltage dc is pulsed into these transformers at very high frequency with a bunch of low-ish voltage MOSFETS. This allows a lot of power to be put through the transformers without requiring a huge iron core. For comparison imagine the size and weight of the transformer you'd need to push 1000w continuously. Probably the size of the entire inverter.

2. The output of the transformers is rectified, possibly by discrete diodes that look like MOSFETS, or in lower power applications could be normal diodes. The thing is at this point, the voltage is around ~170vdc (for 110v inverters) and around ~340vdc for 220v inverters. Note that the dc voltage is higher than the AC voltage because AC voltage is rms, which is a sort of average, but the peak voltage of the sine wave is the DC voltage you're seeing here.

Now the good thing about these high voltages is that to get the 1000w rating, at 120v its only 8-9a going through here, so not as beefy components required in the HV section.
3. In an off-grid inverter you'd have a large-ish capacitor bank to hold the HV and stabilize it, but in a grid tie inverter its not as neccessary because there's no surges and most noise will be supressed later in the circuit.

4. Once you have your HVDC, it goes into an H-bridge, which is always in sets of 4. This is a similar concept to reversing relays, basically they are used to switch the high voltage in a certain way that they can reverse it, so you can get AC from it. Those are the IXFH44N50P transistors you see. They are 500v rated.

5. An SPWM signal is fed into the transistors, to make the output as close to a sine wave as possible. Though it needs a lot of filtering to get rid of all the switching noise.

6. Output of the transistors goes into an LC filter, which is an inductor in series with the output, and a (low capacity) capacitor after the inductor to neutral. This turns the rather noisy sine wave into a basically perfect sine wave (depending on how good the filtering is). Then it just goes out into the utility, and of course there's a lot of microcontrollers in the way, making sure it isn't overheating, outputting when theres no grid, overpowered, or the grid voltage is too high. For example, if the grid voltage is 110v, the inverter will push power in, so it might go up to 110.1v or w/e. If your grid is too weak and your grid-tie inverter is too powerful, it may raise the voltage above acceptable range and a PROPER inverter would realize and either shut down or reduce output. Now with a 1000w inverter I doubt this scenario would happen, although its entirely doable.



But yeah most likely the only difference between the two is the windings of the LV-HV transformers, I'd assume that the higher voltage one has 2x the turns but with thinner wire on the primary side. Secondary is probably the same.

Thats basically the issue with inverters, there's no one-size-fits-all when it comes to voltage ranges. IMO, the higher the voltage the better, because there's less losses the higher you go. That's why you have these solar gridtie inverters that can do 70kw that are smaller lighter and cheaper than 12kw low voltage inverters. But of course thats a different topic b/c going off-grid with high voltage is rather complicated due to having so many batteries in series, and of course the entry cost because you need a large number of solar panels in series to even get started.
Wow, thank you so much, very informative.
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Re: Grid Tie Inverters - What's the difference?

Post by arthur8 »

I have some of those bad boys connected to the output of my 5kVA 48v low frequency inverter. They feed the inverter AC Output and allow me to run bigger things like my 24kBTU A/C unit with my entire home.

Just changed the fans on them, the default one sucks.
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